The present invention generally relates to traction control systems and more particularly relates to a method and a device for controlling the traction slip of a vehicle with a high coefficient of friction.
Traction slip basically means that the wheels rotate faster than what is expected for a given vehicle speed. This condition frequently occurs during starting to drive, especially when the clutch is engaged or when the gas pedal is applied vigorously in low gear. In this event, the drive torque is in excess of the moment which can be transmitted between the wheels and the roadway due to the frictional conditions prevailing between the two.
FIG. 1 is a schematic view of a vehicle from the top, it being assumed that the vehicle has a front-wheel drive. Reference numeral 11 relates to the left front wheel, 12 to the right front wheel, 13 to the right rear wheel, and 14 to the left rear wheel. Consequently, wheels 11 and 12 may encounter traction slip.
A principal aim is the limitation of traction slip. On the one hand, excessive traction slip causes loss in traction because only a comparatively low force can be transmitted between tires and road surface when the wheels spin greatly. On the other hand, major tire wear and driving situations which are not defined optimally in terms of driving stability will occur as a result.
Therefore, attempts have been made by conventional traction slip control systems to limit the traction slip to an optimal value. This can be done by reducing the propulsive power and/or by braking the driven wheels. Adverse effects may be caused thereby in the event that an extremely high torque requirement exists during starting to drive, for example, when starting to drive uphill or starting with a heavy load (baggage, passengers, roof load, trailer). In this case, traction slip is even more likely to occur because the forces or torques to be overcome are higher. Conventional traction slip control systems frequently cause stalling of the engine because the engine with a heavy load is decelerated below the at least necessary rotational speed, either due to engine torque reduction or due to braking with the clutch engaged. Vehicle start is then possible only with the traction slip control system deactivated.
An object of the present invention is to provide a method and a device for traction slip control at a high coefficient of friction which permit the vehicle to start even with a heavy vehicle load.
According to one aspect of this invention, the situation with a comparatively heavy starting load is identified. More particularly, various conditions can be polled or examined in this respect. According to another aspect of the present invention, the identification is followed by taking a countermeasure to the end that instantaneously higher traction slip values are accepted than is in conformity with conventional aims of traction slip control. For example, this may be effected by reducing a brake control intervention and/or by reducing the nominal engine torque decrease or by a nominal engine torque increase.
The traction slip control system according to the present invention may be provided in addition to conventional traction slip control systems. The conventional system basically operates as usual. Only in the event that the start situation described hereinabove is identified will the conventionally generated nominal values or actuating signals for the brake and/or the engine be modified or replaced according to the present invention.